Radio signaling



Oct. 25, 1932.

W. R. BLAIR ET AL RAD IO S IGNALING Filed Nov. 24, 1928 2 SheetsSheetOOOOOOOQOQDDDDDDDDDDD wwwwadcccccccooooooooocoo Try/7501256)" Z77ve77%ra@Zaulu Oct. 25, 1932.

w n 6 .w 7 EA 6 "mg I oooaooooaoooooo oooooaoaooooboon 2 Km r0 0ODJDANDODODDDDD M q no 0 CGCCOCCOGCCCCOC mwsmzz ier 2 2 Fans/ni erPatented Get. 25, 1932 UNITED STATES PATENT OFFlCE WILLIAM.R. BLAIR ANDLOUIS COHEN, OF WASHINGTON, DISTRICT OF COLUMBIA RADIO SIGNALINGApplication filed November 24, 1928. Serial No. 321,688.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928; 3700. G. 757) The invention described herein may be manufactured and usedby or for the Government for governmental purposes, without the paymentto us of any royalty thereon.

.5 This invention relates to the art of radio signaling and moreparticularly to improved methods in the transmission of radio signals.

One of the objects of this invention is the elimination of harmonicfrequencies in the transmission of radio signals.

Another object is the reduction to a minimum of the width of thefrequency band occupied bya transmitter in the emission of signals.

A further object is to provide means for the simultaneous transmissionof several radio signals of different frequencies from a single antenna.

In the production of electrical oscillations by the three electrodevacuum tube method,

and this is the method most generally used in practice at the presenttime, it is very difficult to produce oscillations of a pure sine waveform of a single frequency. The oscillations produced are generally of adistorted wave form, that is the oscillations comprise a fundamentalfrequency and harmonic frequencies. Also the fact that an antenna, whichis an oscillator of an infinite number of degrees of freedom and cantherefore respond resonantly to many frequencies, forms part of thetransmitting oscillating system, helps to give emphasis to the harmonicsin the radiation from the antenna. The useful signal transmissionrequires, of course, oscillations of one frequency only, and thetransmission of the harmonic frequencies is an unnecessary cause ofinterferences, not serving any useful purpose whatsoever; it does notcontribute in any way to the efficiency of transmission.

The presence of harmonics in the transmission of signals is veryobjectionable because of interference caused on other frequenciesbesides the one on which the signal is transmit- ,45 ted. Many attemptswere made to remedy or at least to mitigate this evil, such as the useof amaster oscillator, filter circuits, and other devices, but it isfound in practice that even with the aid of these improvements the har--monies are not completely eliminated, and in some methods the apparatusrequired is too complicated for general use.

This invention contemplates a novel circuit system whereby theoscillations of the transmitter are impressed on'the antenna through theintermediary of a wave conductor, that is a conductor of distributedinductance and capacity on which a wave development is effected, andsuitably adjusted in relation to the fundamental frequency of thetransmit- 6Q ter oscillations. By this means the oscillations of thefundamental frequency only are impressed on the antenna, or a wire asthe case may be, and the radiation is free from harmonics. This methodalso offers a convenient means for the simultaneous transmission ofseveral signals of difierent frequencies from a single antenna or over asingle Wire. The method is best understood by referring to theaccompanying drawings which form part of this specification in whichFigure 1 shows diagrammatically an embodiment of the invention in whichthe trans- ,mitter is connected to a wave conductor and a tuned antennacoupled to the wave conductor. i

Figure 2 shows a modification of the invention in which an untunedantenna is used.

Figure 3 is similar to Figure 2' except that the wave conductor isgrounded. 0 Figure 4 is an embodiment of the invention showing thesimultaneous transmission of two signals of different frequencies from asingle antenna.

Figure 5 shows an embodiment oftheinvention illustrated in Figure 2 inits application to the transmission of signals over wires.

Having particular reference to the drawings in which similar numbersdesignate the same parts in all of the drawings, in Figure 1 1 thetransmitter 1, which is preferably of the vacuum tube type, isassociated with an oscillatory circuit 2, 3. The oscillatory circuit isconnected at t to the metal shield 6, 6 which is placed in closeproximity to the wave coilv 5, 5; The wave coil 5, 5 and metal shield 6,6 as well as the coupling coil 7 are all shown in this figure in crosssection. The wave coil 5, 5 Which is preferably in the form of asolenoidal coil, though it may be any other form 1 9 of coil, togetherwith the metal shield 6, 6 forms a wave conductor that is one ofdistributed inductance and capacity and of sutlicient length in relationto the wave length of the transmitted oscillations to assure a wavedevelopment thereon. An adjustment of the wave conductor is effected byvarying the distance separation of the metal shield 6, 6 from the wavecoil 5, '5. The metal shield 6, 6 may be in the form of semi-cylinderspartially surrounding the wave conductor or preferably flat plates. Acoupling coil 7 is placed within the wave coil 5, and this coupling coil7 is connected in series in the antenna which comprises also in series avariable condenser 9, a loading coil 10 and ground 11. By the propertuning of the antenna and suitably adjusting the wave conductor, that isthe distance separation of the metal shields from the wave coil, all inrelation to the frequency of the transmitter, an adjustment is effectedwhereby considerable current is transmitted to the antenna, and only ofa single frequency that of the fundamental frequency of the transmitter.In actual test it was found that with this arrangement the harmonics,though very pronounced in the transmitter, could not be detected in theantenna even by coupling a wave meter close to the antenna.

- Figure 2 shows an embodiment of the in vention by which the sameresults are accomplished with an untuned antenna. Here the point 4 ofthe oscillating circuit 2, 3 is connected to one end 13 of the wave coil5, 5 and the antenna 8 is connected to the metal shield 6, 6 at point12. The only adjustment'requiredjn this arrangement is the varying ofthe distance separation of the metal shield 6, '6 from the wave coil5,5. With this ar- -mgement it is also found that the oscillations inthe antenna are completely free from harmonics, the oscillations in theantenna are only those of the fundamental frequency of the transmitter.

The arrangement shown in Figure 3 differs from Fi ure 2 only in onedetail and that is that t e other end of the wave coil is grounded.Results similar to those obtained b the arrangement shown in Figure 2are a obtained with the arrangement shown in Figure 3.

The systems shown in both Figure 2 or 3 have a great advantage in thatthe antenna is nn tuned, simplifying considerably the adgstmentsrequired and also affording therea convenient means for multiplextransmission, that is operating several transmitters of differentfrequencies on the same antenna. This is shown in Figure 4 in which,

" for the purpose of illustration, only two transmitters are shownassociated with one antenna. The oscillating circuit 15 associated withtransmitter 14 is connected first at 18, and then at 19 to the wave coil16, 16

and its metal shield 17, 17'is connected at 20 to the antenna 21.Similarly the oscillating circuit 23 associated with transmitter 22 isconnected to the latter at 24 and then at 25 to the wave coil 26, 26 andits metal shield 27, 27 is connected to the same antenna 21 as at 28.The wave conductors 16, 16; 17 17 and 26, 26; 27, 27 are each separatelyad justed in relation to the frequencies of the respective transmitterassociated therewith. Additional transmitters associated with properlyadjusted wave conductors could be connected on to the same antenna, thusaffording a means for the simultaneous transmission of several signalsof different frequencies from a single antenna.

Itis obvious that this system is also applicable for the transmission ofsignals over wires as the connecting of the transmitting station with areceiving station by means of a wire amounts simply to the extension ofthe antenna to reach from one station to the other. Since in thisarrangement the tuning is altogether independent of the antenna, it isobvious that the antenna may be lengthened to any degree desired andthus obtain the desired condition of wire transmission. This is shown inFigure 5 which differs from that shown in Figure 2 only in that in placeof the transmitting antenna, the transmitting circuit is connected to awire 29 which extends all the way to a receiving station 30.

We claim:

1. In a system for the transmission of radio signals comprising anoscillation energy source associated with an oscillating circuit, awaveconductor and an antenna, said wave conductor comprising a wave coil anda metal shield in proximity thereto, said oscillatin circuit beingconnected at one point to said metal shield, said wave coil being openat both ends, a coupling coil which is coupled to said wave coil beingconnected in series in said antenna.

2. In a system for the transmission of radio signals comprising anoscillation energy source associated with an oscillating circuit, a waveconductor and an antenna, said wave conductor comprising a wave coil anda metal shield in proximity thereto, said oscillating circuit beingconnected at one point to said metal shield, said wave coil being openat both ends, a coupling coil which is coupled to said wave coil beingconnected in series in said antenna, said an tenna comprising in itscircuit a variable condenser and loading coil by which the antennacircuit is adapted to be tuned for the frequency of the oscillations ofthe transmitter.

3. In a system for the transmission of radio signals comprising anoscillation energy source associated with the oscillating circuit, awave conductor and antenna, said wave conductor comprising a waveco'il'and a metal shield in proximity thereto, said oscillating circuitbeing connected at one point to said metal shield a coupling coil whichis coupled to said Wave coil being connected in series in said antenna;the frequency of the oscillation source being adjusted for res onance tothe natural period of the said wave coil.

4. In a system for the transmission of radio signals comprising anoscillation energy source associated with the oscillating tures.

WILLIAM R. BLAIR. LOUIS COHEN.

